Embodiments of the present disclosure relate to a turbine engine equipped with an epicyclic reduction gear train. The prior art includes U.S. Patent Application Publication No. 2015/0337677 A1 to Roberge, and U.S. Pat. No. 4,651,521 to Ossi, both of which are hereby incorporated by reference in their entireties.
A twin-spool dual-flow turbine engine generally comprises a plurality of compressor stages, in particular a low-pressure (LP) compressor and a high-pressure (HP) compressor, which are disposed in the primary flow path of the engine. Upstream of the low-pressure compressor there is disposed a wheel with movable blades of large size, or fan, which supplies both the primary flow that passes through the LP and HP compressors and the cold flow, or secondary flow, which is directed directly towards a cold-flow nozzle, known as a secondary nozzle. The fan is driven by the rotary shaft of the LP body and usually rotates at the same speed as that shaft. However, it may be worth making the fan rotate at a lower rotation speed than that of the drive or LP shaft, particularly when the fan is very large, with the aim of improving its aerodynamic adaptation. For this purpose there is a reduction gear between the LP shaft and a fan shaft, which carries the fan.
Among the types of reduction gears used are epicyclic reduction gears, which have the advantage of offering significant rates of reduction in the speed of rotation, within limited amounts of space. These reduction gears are characterised by a sun gear which drives planet pinions that roll on an outer ring gear while rotating about planet spindles carried by a planet carrier.
Conventionally, an aircraft requires electrical energy and hydraulic energy from a turbine engine, as well as thrust. In traditional turbine engines, this power is taken off mechanically from the HP shaft in order to drive the input shaft of an accessory gear box (AGB) placed on a housing of the turbine engine. This input shaft is driven in rotation by a transmission shaft driven by a pinion integral with the HP shaft.
The current trend aims to increase the electrical power to be provided to the aircraft, and therefore the take-offs of mechanical power from the engine. Studies conducted previously have shown that a take-off of mechanical power performed entirely on the HP shaft was too restrictive from an engine operability point of view. This is because too high a take-off of mechanical power has a negative effect on the operability of the HP body, in particular when the engine is operating at low speed. The solution of a take-off of mechanical power distributed between the HP shaft and the LP shaft would largely allow engine performance and operability to be restored.
Mechanical distribution solutions exist (epicyclic gear train, two-speed accessory gearbox, clutch, etc.—see French publication FR 2882096 A1, for example) but they are problematic because of the size of the resultant single generator and the complexity of transmitting both speeds towards the space accommodating this generator. This is because recent engines tend to have thin nacelles, which means placing the AGB in the engine compartment (space between the primary flow path and the secondary flow path). As the volume of this zone is very limited, it is difficult to install one or more large generators there without having an impact on the lines of the secondary flow path and thus on the fuel consumption of the engine. In addition, this zone is close to the hot portions of the engine and so it limits the lifespan of the generators.
One of the lines of research for these engines is therefore to succeed in placing additional generators on the engine without having an impact on the aerodynamic lines. A generator can be “buried” in the turbine engine as in International Publication No. WO 2007/036202 A1, but this results in very complex maintenance and considerable environmental constraints. This is also the case for a generator installed in the tail cone or nose cone of a turbine engine.
One solution would be to install this generator in the fan, in the nose or upstream cone. The problem with such an installation would be the following: there is no fixed portion on which the stator can be made to rest in this space. The solutions would therefore be limited to:
either making a rotating stator, connecting the stator (or the rotor) to the LP shaft and the other to the HP shaft. In this way, electricity can be produced, but it is problematic to get it out. This is because the rotating contacts that allow the transition from a rotating point or marker to a fixed point or marker are often complex or voluminous or have a short lifespan. The gear trains could be routed to the inside of the HP shaft, but this involves bringing them out through the tail cone and therefore subjecting them to its environmental stresses. In French publication FR 3017413 A1, for example, the equipment (a pump) is installed inside bearings supporting the fan, upstream of the reduction gear and upstream of the fan. The drive speed of the pump is the difference in speed between the input and the output of the reduction gear. The configuration of the reduction gear involves a fixed ring gear and a movable planet carrier driving the fan in rotation;
or being able to bring an element of the housing inside the nose cone. In a conventional engine, the only way to do this would be to bring it via the rear of the engine through the HP shaft, but this has a large number of disadvantages (rigidity, weight, and exposure to the high temperatures of the tail cone).
Another solution would be to add a structure fixing the nose cone to the fan housing to hold the stator. In French publication FR 2919896 A1, a generator is fitted in the cone, the rotor of which is the LP shaft and the stator of which is a fixed element of the fan cowl. In a conventional engine, this cowl cannot be accessed from the interior of the nose cone. The solution described is the addition of radial stay arms between the nose cone and the fan housing.
Embodiments of the present disclosure bring in particular a simple, effective and economical solution to the above problem of the prior art, in the case of a turbine engine with an epicyclic reduction gear train.